This invention relates generally to washing machines, and more particularly, to methods and apparatus for controlling wash temperatures.
Washing machines typically include a cabinet that houses an outer tub for containing wash and rinse water, a perforated clothes basket within the tub, and an agitator within the basket. A drive and motor assembly is mounted underneath the stationary outer tub to rotate the basket and the agitator relative to one another, and a pump assembly pumps water from the tub to a drain to execute a wash cycle.
At least some known washing machines provide that an operator can select from three wash temperatures. Such machines have valve systems including hot and cold water valves. For a hot wash operation, for example, the hot water valve is turned on, i.e., opened, and for a cold wash operation, the cold valve is opened. For a warm wash, both the hot valve and cold valve are opened. The flow rates of water through the valves is selected so that the desired warm temperature is achieved using hot and cold water.
The use of a pressure sensor to measure water level allows for more accurate control of multiple water levels compared to the use of a pressure switch. Unfortunately, this provides an opportunity for a single point error in the microprocessor hardware, or software to generate an over fill condition. At least one known system externally monitors the pressure sensor signal and generates a signal that opens a relay that breaks the line voltage to the water valve. The use of a relay adds a cost to the circuit.